1. Field of the Invention
The present invention relates to a lead cartridge with an openable capping structure, for so-called cartridge type mechanical pencils.
2. Description of the Prior Art
Recently there has been proposed a so-called cartridge type mechanical pencil, such as illustrated in FIG. 1, in which the lead cartridge is changed for another one for changing the leads being used for leads or for replenishing the mechanical pencil with leads, instead of changing or supplying the leads individually, so that the leads are changed for different leads or the mechanical pencil can be replenished with leads without soiling the hand.
In changing leads or supplying leads to the conventional cartridge type mechanical pencil, a cap 1 covering the open end of a lead cartridge 2 is removed and thrown away, and then the lead cartridge 2 is fitted in the cylinder of the mechanical pencil with the front end open. Accordingly, the leads contained in the lead cartridge 2 are liable to fall off the lead cartridge 2 if the open end of the lead cartridge is directed downward even slightly. Therefore, in fitting the cartridge 2 in the cylinder, the lead cartridge must be held with the open end thereof directed upward and to be fitted carefully into the cylinder or the mechanical pencil.
On the other hand, in removing the lead cartridge 2 from the cylinder 3, the leads slip off the lead cartridge 2 if the open end of the lead cartridge 2 is directed downward even slightly, and hence remain in the cylinder 3.
Furthermore, as illustrated in FIG. 2, the conventional mechanical pencil accommodates the lead cartridge 2 containing a plurality of leads, and a lead guide 7 detachably holding the lead cartridge 2 in the cylinder 3 thereof, and the residual leads are returned into the lead cartridge 2 in removing the lead cartridge 2 from the cylinder 3. Therefore, the inner surface of the open end of the lead cartridge 2 needs to be tapered to form a taper surface 21 and an inner expansion 31 needs to be formed in a portion of the cylinder 3, so that the inside diameter of the cylinder is reduced partly in a portion corresponding to the inner expansion 31 limiting the outside diameter of the lead cartridge 2, and thereby the capacity of the lead cartridge 2 is reduced. Furthermore, since it is impossible to form such a cylinder 3 having such an inner expansion 31 through extrusion molding, the cylinder 3 needs to be formed through injection molding, which requires a molding die which is more expensive than that for extrusion molding.